During the machining of hollow thin-walled parts, for example sleeves, which are machined only on their outer side but not on their inner side, there is the problem that the unmachined inner side used for clamping the part has shape errors, for example non-roundness, generally in conjunction with non-uniform wall thickness in the circumferential direction or deviations from the straight cylindrical shape, under certain circumstances likewise in conjunction with wall thickness differences in the longitudinal direction. If a conventional clamping device is used, the parts are deformed elastically when being clamped in, on account of these shape errors of their inner side. As a result, during the machining of the parts, the shape errors of the inner side are, so to speak, transferred to the outer side. Therefore, it is not possible to achieve either high shape accuracy or a very high surface quality, and in addition cylindricity can barely be maintained. Therefore, the lower the wall thickness and the greater the length of the parts, the less consideration is given to clamping such thin-walled parts at their two end faces since they then deviate more or less severely under the cutting forces. In addition, the parts then tend to oscillate, so that chatter marks are additionally produced.
The invention is based on the object of providing a clamping device with which, primarily, very thin-walled and relatively long parts can be clamped satisfactorily, largely independent of irregularities of their inner surface, and their outer side can be machined with the required accuracy and surface quality. According to a preferred embodiment of the present invention, a clamping device may have the following features: there is a clamping spindle (11) which, at least at one end, is provided with coupling elements (12) for coupling to the main spindle of a machine tool, the clamping spindle (11) has a first supporting face (17) at one end which is aligned axially and faces the other end of the clamping spindle (11) and which is arranged on the clamping spindle (11) such that it cannot be displaced in the axial direction; there is a second supporting face (21) on the clamping spindle (11) at the other end, which is aligned axially and faces the one end and which is arranged on a clamping element (19) which is guided on the clamping spindle (11) such that it can be displaced in the axial direction; there is a clamping device (15), by means of which the clamping element (19) with the second supporting face (21) can be displaced relative to the first supporting face (17) and can be fixed while applying an axial clamping force to the clamping spindle (11); there is at least one clamping sleeve (13), which is produced from an elastomer, whose inner diameter is matched to the outer diameter of the clamping spindle, whose end faces are matched to the first supporting face (17) and to the second supporting face (21); a clamping sleeve (13) has a plurality of supporting strips (23) on its outer side, which are produced from a metallic material, which are permanently connected to the clamping sleeve (13), which are arranged distributed uniformly on the circumference of the clamping sleeve (13) and whose outer side (29) forms a cylinder surface section in each case which is matched to the inner diameter of the part (24).
Similar problems also occur during the machining of the inner side of thin-walled parts whose outer side remains unmachined, in particular when the parts are relatively long. The invention is therefore also based on the object of providing a clamping device with which, primarily, very thin-walled and relatively long parts can be clamped satisfactorily, largely independent of irregularities of their outer surface, and their inner side can be machined with the required accuracy and surface quality. In a preferred aspect of the present invention, the clamping device (15) is formed by a longitudinal section (18) of the clamping spindle (11) that is provided with an external thread and by a clamping ring (19) matched thereto and having an internal thread.
The fact that, instead of rigid clamping jaws, a clamping sleeve made of an elastomer is used and is guided on a smooth cylindrical clamping spindle and is compressed axially via its two end faces means that the quasi hydraulic behavior of the material of the clamping sleeve is utilized in order to compensate to a large extent for irregularities in the clamping surface of the part. The fact that there are metallic supporting strips on the outer side of the clamping sleeve means that abrasion of the clamping sleeve is avoided when the parts are pushed on and pulled off and, as a result, a higher lifetime of the clamping device and, at the same time, constant clamping security and clamping accuracy are achieved.
The clamping device may be adapted more easily to different lengths of the parts. In a preferred aspect, there are a plurality of clamping sleeves (13), which are axially displaceably guided on the clamping spindle (11) and which are arranged between the first supporting face (17) on the clamping spindle (11) and the second supporting face (21) on the annular clamping element (19).
In another aspect, the axial frictional force which occurs when the clamping sleeves are being clamped, between the clamping sleeve and its seating surface on the clamping spindle or on the basic body, is distributed over a plurality of relatively short sections where said force is lower, individually and overall. As a result, the radial clamping force of the clamping device is also distributed, at least approximately uniformly, over the entire clamping length. The fact that the clamping sleeve is designed to be shorter than its supporting sleeve and does not project beyond the end faces of the supporting sleeve, and that the transmission of the axial clamping force is performed by interposed pressure rings prevents the compliant clamping sleeves being pressed into the initially open interspaces between the supporting sleeves and damaged in the process at the start of the clamping operation. In a preferred aspect, for each clamping sleeve (13) there is a supporting sleeve (14), which is produced from a material whose dimensional stability is greater than the dimensional stability of the clamping sleeve (13), whose inner diameter is matched to the outer diameter of the clamping spindle (11) and to whose outer diameter the inner diameter of the clamping sleeve (13) is matched; the supporting sleeves (14) may have a greater length than the clamping sleeves (13); each clamping sleeve (13) may be arranged on its supporting sleeve (14) in such a way that each of the end faces of the clamping sleeve (13) does not project in the axial direction beyond the end faces of the supporting sleeve (14); a pressure ring (25) may in each case be arranged between two successive clamping sleeves (13), whose inner diameter is matched to the outer diameter of the supporting sleeves (14) and whose outer diameter is at most equal to the inner diameter of the part (24).
In another aspect, when the clamping device is operated, the clamping sleeves can be compressed only by the differential amount of the length dimensions. This results in an exactly defined radial clamping force and, in addition, as a result overstressing both of the elastic clamping sleeves and of the thin-walled parts is avoided. In a preferred aspect, the sum of the axial extent of the pressure ring (25) and of the clamping sleeve (13) is greater by a predefined amount (26) than the axial extent of the supporting sleeve (14) of the latter.
In another aspect, the number of components of the clamping device is reduced. In a preferred aspect, each pressure ring (25) is detachably or non-detachably connected to the end of a supporting sleeve (14), preferably produced in one piece with it.
In another aspect, the radial diameter change of the clamping sleeve is disproportionate to the axial compression movement. The same applies to a configuration according to claim 8 and according to claim 18, respectively, a greater transmission factor between the radial diameter change and the axial compression movement being achieved. In a preferred aspect, on the clamping spindle, the seating face for each clamping sleeve is formed as the outer surface of a truncated cone, which widens toward the first supporting face, and the inner face of the clamping sleeve is matched to its seating face. In another preferred aspect, on the supporting sleeve (27), the seating face (28) for the clamping sleeve (31) is formed as the outer surface of a truncated cone, and the inner face (32) of the clamping sleeve (31) is matched to its seating face (28) on the supporting sleeve (27).
In another aspect, the clamping spindle or the base body can be supported at its second end, so that it gives way elastically to a lesser extent under the cutting forces and, as a result, the machining accuracy remains constant over the entire length of the part. In a preferred aspect, at its end facing away from the coupling elements (12), the clamping spindle (11) has an outer and/or an inner accommodation face (55; 56) for a supporting device (57).
In another aspect, a clamping device which can be produced and operated relatively simply is provided. In a preferred aspect, the clamping device (15) is formed by a longitudinal section (18) of the clamping spindle (11) that is provided with an external thread and by a clamping ring (19) matched thereto and having an internal thread.